Failover Clustering Versus Database Mirroring

SQL Server 2005 Enterprise Edition will support two primary mechanisms for implementing database redundancy and failover strategies to achieve high availability. SQL Server 2005 continues to support Microsoft Cluster Services (MSCS), the main failover and redundancy technology used in previous versions of SQL Server. MSCS is a failover solution for a cluster of machines; when one machine in the cluster fails, client applications are redirected to another machine in the cluster in a way that is transparent to the client applications.

In addition, SQL Server 2005 introduces a feature called database mirroring, which will be available in the first half of 2006. Mirroring maintains copies of a database on separate servers (called the primary and mirror), allowing applications to switch to the mirror SQL Server in the event of a server or database failure in the primary.

Similar Goals, Different Implementation

Although database clustering and mirroring both increase database availability via redundancy, the technologies differ in their implementation details and one may be better than the other for specific scenarios.